This invention relates generally to a method of constructing an expandable tubular stent from a flat wire or ribbon. More particularly, the present invention is directed to such a stent formed from an elongate ribbon having portions cut therefrom where the cut ribbon is wound into a cylindrical stent configuration.
It is well known to employ various endoprostheses for the treatment of diseases of various body vessels. One type of endoprosthesis is commonly referred to as a stent. A stent is a generally longitudinal tubular device formed of biocompatible material which is useful in the treatment of stenosis, strictures or aneurysms in body vessels such as blood vessels. These devices are implanted within the vessel to reinforce collapsing, partially occluded, weakened or abnormally dilated sections of the vessel. Stents are typically employed after angioplasty of a blood vessel to prevent re-stenosis of the diseased vessel. While stents are most notably used in blood vessels, stents may also be implanted in other body vessels such as the urogenital tract and bile duct.
Stents generally include an open flexible configuration. This configuration allows the stent to be inserted through curved vessels. Furthermore, this configuration allows the stent to be configured in a radially compressed state for intraluminal catheter implantation. Once properly positioned adjacent the damaged vessel, the stent is radially expanded so as to support and reinforce the vessel. Radial expansion of the stent may be accomplished by inflation of a balloon attached to the catheter or the stent may be of the self-expanding variety which will radially expand once deployed. Structures which have been used as intraluminal vascular grafts have included coiled stainless steel springs; helically wound coil springs manufactured from a heat-sensitive material; and expanding stainless steel stents formed of stainless steel wire in a zig-zag pattern. Examples of various stent configurations are shown in U.S. Pat. Nos. 4,503,569 to Dotter; U.S. Pat. No. 4,733,665 to Palmaz; U.S. Pat. No. 4,856,561 to Hillstead; U.S. Pat. No. 4,580,568 to Gianturco; U.S. Pat. No. 4,732,152 to Wallsten and U.S. Pat. No. 4,886,062 to Wiktor.
Flexibility is a particularly desirable feature in stent construction as it allows the stent to conform to bends in a vessel. Many of the stent configurations presently available are formed of a plurality of aligned, expandable, relatively inflexible, circular segments which are interconnected by flexible elements to form a generally tubular body which is capable of a limited degree of articulation or bending. It has been found, however, that certain stents promote binding, overlapping or interference between adjacent segments on the inside of a bend due to movement of the segments toward each other and into contact. Also, on the outside of a bend, segments can move away from each other, leaving large gaps, leading to improper vessel support, vessel trauma, flow disturbance, kinking, balloon burst during expansion and difficult recross for devices to be installed through already implanted devices and to unsupported regions of the vessel.
Accordingly, it is desirable to provide an expandable tubular stent which exhibits sufficient radial strength to permit the stent to maintain patency in an occluded vessel and yet be capable of elongation by affixing multiple stent segments thereto. The present invention prevents reoccurrence of occlusions in a passageway and prevents recoil of a vessel wall by providing an expandable tubular stent of generally open, cylindrical configuration that utilizes reduced thickness struts. Such a stent prevents recoil of body passageway walls and allows elongation of the stent to prevent migration of the stent within a luminal structure.
It is an object of the present invention to provide an improved intraluminal prosthetic device that will hold open an occluded, weakened or damaged vessel.
It is a further object of the present invention to provide a spiral wound stent capable of self-expansion within a vessel into which it is implanted.
It is still a further object of the present invention to provide a longitudinally flexible stent of open configuration that exhibits improved radial and longitudinal flexibility in both the stent body segments and in the flexible joints between the segments.
It is yet another object of the present invention to provide a method of forming such a longitudinally flexible stent from a flat wire or ribbon of biocompatible material which is cut and spirally wound over a cylinder to form a tubular stent.
It is still another object of the present invention to form at least one connector on each such stent and attach each connector so as to form a longitudinal succession of stent segments.
In the efficient attainment of these and other objectives, the present invention provides a self-expanding tubular stent comprising a plurality of stent segments. Each stent segment is formed of an elongate ribbon having portions cut therefrom to form a wave-like undulating pattern, opposed edges of which are attached to one another so as to form a generally cylindrical configuration. A disclosed method effects formation of such an expandable tubular stent by first providing an elongate flat ribbon of biocompatible stent material and selectively removing portions of such material to form an undulating wave-like pattern along the length of the ribbon. The ribbon is then wound into a generally cylindrical configuration, and opposed ends of the ribbon are secured to one another to form a generally cylindrical and expandable spiral stent section. After forming a plurality of such stent sections, the stent sections are arranged in longitudinal succession and interconnected so as to form an elongated stent configuration.